Rome, the birthplace of nuclear physicist Enrico Fermi, is this week hosting a conference dedicated to discussing results from the NASA satellite that bears his name. Some 400 scientists have gathered in the Italian capital to discuss what the Fermi Gamma-Ray Space Telescope, launched in June 2008, can tell us about all manner of extreme celestial events – from the accretion of matter by supermassive black holes and ultra-energetic events known as gamma-ray bursts to the hypothesized collision of dark-matter particles.

First up on to the vast stage of the echoey Aula Magna at La Sapienza University was NASA’s Elizabeth Hays, who gave an overview of Fermi’s progress to date. Hays says she was happy to report that Fermi’s operations were “becoming almost mundane”, now that the satellite has been circling the Earth for over 1000 days, completing more than 16,000 orbits in that time, and collecting vast quantities of gamma-ray data in the process. (There is even now a Fermi app for the iPhone/iPad.)

Some of the gamma rays collected by Fermi have their origins on Earth, with Hays pointing out that radiation generated by charged particles during thunderstorms created something of a minor storm of their own on the Web with nearly half a million views of a NASA video explaining the process (see video above). Fermi’s principal source of gamma radiation is, however, outer space, and it surveys almost the whole sky in three hours, making increasingly detailed studies of bright sources and attempting to pinpoint the nature of weaker ones.

The first catalogue of distinct gamma-ray sources revealed by Fermi was released about a year ago and researchers have been working furiously to get a second, more precise catalogue published. As Dave Thompson of NASA’s Goddard Space Flight Center explained, this has taken a lot longer to produce than expected but he argues that when it comes out later on this month it will represent a “major revision” of the old catalogue, listing some 1888 active galactic nuclei and other gamma-ray sources.

Many of those who have made the trip to Rome will also be hoping that another high-profile – and very expensive – astroparticle mission will finally get to make the trip into space in the next few days or weeks. That mission is the cosmic-ray observatory known as the Alpha Magnetic Spectrometer, which is expected to launch on 16 May on the space shuttle Endeavour. As speaker Giovanni Bignami of the University of Pavia put it, “we are keeping our fingers crossed”.

Last week Italy’s energy agency ENEA put on a conference to celebrate the 50th birthday of its Casaccia research centre outside Rome. The occasion also marked the official restart of two veteran research reactors at the site, which, said the agency, represented the symbolic return of nuclear power to the country. A referendum held in the wake of the Chernobyl disaster in 1986 led to all of Italy’s power reactors being shut down, but the current government announced two years ago that it was to return to the nuclear fold and start construction of a number of modern plants by the end of 2013.

There are still many people in Italy who oppose nuclear power, notwithstanding its newfound green credentials. And there are also plenty who believe that the government’s ambitious plans, ultimately to generate 25% of the country’s electricity from nuclear, are destined to become an expensive flop. Certainly, the meeting at Casaccia did not instill confidence.

Being a 50th birthday party, it was natural that scientists and engineers should take a look back at the early days of Italy’s nuclear programme, entertaining us with film clips that re-enacted some of the crucial events leading to Italian physicist Enrico Fermi’s operation of the world’s first nuclear reactor in 1942. But in all the various talks there seemed precious little to indicate that concrete steps are being taken to revive nuclear. Indeed, the politician in charge of Italy’s energy policy, Stefano Saglia, was supposed to come and tell us about the new nuclear programme, but he failed to show up.

Although Casaccia focused predominantly on renewable energies and the environment throughout the 1990s it never entirely left behind its nuclear roots. In particular, it continued to operate two research reactors, the 1 megawatt thermal reactor TRIGA and the 5 kilowatt fast reactor TAPIRO. And it is the restart of these devices, following a two-year period of maintenance, that ENEA boss Giovanni Lelli declared on Wednesday marks the symbolic return to nuclear. But in fact it seems more of a case of business as usual.

TAPIRO will carry out tests that should help in the design of future generation-IV reactors and could also provide useful data in the construction and operation of the generation-III plants that Italy wants to start building in the next few years. But by and large the two reactors seem set to carry on doing what they have done for many years – developing nuclear medicine, providing isotopes to hospitals and industry, and analysing a range of materials. All laudable activities, but nothing to do with building new power stations. While being shown around a 50-year-old reactor, particularly one that gives off an eye-catching blue glow (see above), is fun, it does not provide convincing evidence that in a few years’ time Italians will once again enjoy the benefits of homegrown nuclear energy.

Whether string theory can tell us anything about reality is a moot point. In the last two or three years this purported “theory of everything” – in principle unifying gravity with the three other forces in nature – has been given a kicking by certain scientists who see it as a kind of intellectual play thing that makes no testable predictions. See What Gina says.. for a taste of that debate.

Certainly the names of some of the talks at the world’s leading string-theory conference, Strings 2009, held in Rome this past week, were on the abstract side. “Holography and the S-Matrix”, “Superconducting black holes”, and “Stringy instantons and duality” give some flavour of the discussions held among the roughly 500 participants at the five-day conference. The fact that the meeting was held at the Pontifical University of Saint Thomas Aquinas only seemed to reinforce its other-worldliness.

But help was on hand for outsiders wanting to try and understand what on Earth this all means. Earlier today, particle physicist grandee Nicola Cabibbo introduced the curious of Rome to two of the big names of string theory – Edward Witten and Brian Greene. Witten, widely regarded as the leading figure in string theory, introduced himself with a few words of Italian and then told the audience what physicists hope to discover when they finally, hopefully, switch on the Large Hadron Collider at the CERN laboratory in Geneva this autumn.

In addition to the expected Higgs boson, the endower of all mass, Witten said that within the debris of particle collisions at the LHC might also be evidence of dark matter and of supersymmetry, which says that a whole slew of new fundamental particles must exist for there to be balance in the subatomic world. And one of the intriguing things about supersymmetry is that it could provide some kind of evidence for string theory.

It was at this point that Witten handed the baton to Greene. Greene is well known for his popularization of science, and with good reason. With some snazzy graphics and his flair for performing, he told us why it is so hard to come up with a theory of quantum gravity, explaining that the smooth variation of space-time as described by general relativity “runs headlong” into the turbulent, chaotic world of quantum mechanics. Postulating that the ultimate constituents of matter are tiny lengths of string, whose different modes of vibration correspond to different fundamental particles, is one way of resolving this problem, he went on, because such strings are like spread-out points that smooth the wild undulations at the smallest scale.

This model, however, has some very odd implications. Greene pointed out that string theory requires an extra 6 (or 7) dimensions of space in addition to the three that we are aware of. Helpfully, these dimensions are so small that we can’t see them, but unhelpfully there are rather a lot of ways of curling these extra dimensions up – some 10500 different ways as it turns out. And we would have to study all 10500 if we want to find out whether or not string theory describes the real world.

For Greene, all is not lost, however. He pointed out that 10500 is somewhat bigger than 10120, and that’s a measure of how much we don’t understand dark energy. In a nutshell he argued that if we happen to live in one of the few of the 10500 universes where conditions are just right for us to exist then there’s a damn good chance that we could have such an apparently statistically unlikely dark energy. For Greene, this suggests we might be on the right lines with string theory. Others may be less convinced.